public class HashBuck {
    static class Node {
        public int key;
        public int val;
        public Node next;

        public Node(int key, int value) {
            this.key = key;
            this.val = value;
        }
    }

    public Node[] array;
    public int usedSize;

    public static final double LOAD_FACTOR = 0.75;

    public HashBuck() {
        array = new Node[10];
    }

    public void put(int key, int val) {
        int index = key % array.length;
        Node cur = array[index];
        while (cur != null) {
            if (cur.key == key) {
                cur.val = val;
                return;
            }
            cur = cur.next;
        }
        // 采用头插法进行插入
        Node node = new Node(key, val);
        node.next = array[index];
        array[index] = node;
        usedSize++;
        if (calculateLoadFactor() >= LOAD_FACTOR) {
            // 扩容
            resize();
        }
    }

    public int get(int key){
        int index = key % array.length;
        Node cur = array[index];
        while (cur != null){
            if (cur.key == key){
                return cur.val;
            }
            cur = cur.next;
        }
        return -1;
    }

    private void resize() {
        Node[] newArray = new Node[2 * array.length];
        for (int i = 0; i < array.length ; i++) {
            Node cur = array[i];
            while (cur != null){
                // 保留cur.next
                Node curNext = cur.next;
                int index = cur.key % newArray.length; // 找到了在新的数组当中的位置
                cur.next = newArray[index];
                newArray[index] = cur;
                cur = curNext;
            }
        }
        array = newArray;
    }

    // 计算负载因子
    private double calculateLoadFactor() {
        return usedSize * 1.0 / array.length;
    }

}
